The hacker says he has control over a number of websites, including other military sites, government sites, and those belonging to universities, said Noa Bar-Yosef, Imperva senior security strategist. Prices range from $33 to $499, depending on how important or widely used the website is. "You can actually buy the capability of being the administrator of the website," she said.

The hacker is also selling databases of personal information he's stolen from the websites for $20 per thousand records, she said. That data could be used by spammers, or by fraudsters to break into online accounts.

Bar-Yosef saw evidence that administrative privileges for 16 sites were for sale. In one case, the hacker is selling data on 300,000 people, taken from the site.

Whoever is selling this stuff probably broke into these websites using a common Web attack called SQL injection, Bar-Yosef said. For years now, hackers have been scanning the Web looking for poorly written Web pages, specifically ones with search boxes or data-entry forms that connect with back-end databases. Then, they try to sneak database commands in through those pages.

With automated tools it's easy for even non-technical hackers -- sometimes called "script kiddies" -- to pull off this type of attack.

When SQL injection works, the results can be devastating. It's what notorious hacker Albert Gonzalez used to break into companies such as Heartland Payment Systems and 7-Eleven.

Imperva redacted the names of the victims from its blog post, but security blogger Brian Krebs has posted more details of the incident, including the names of many of the hacked sites. They include the U.S. states of Utah and Michigan, the government of Italy and the Department of Defense Pharmacoeconomic Center, which analyzes the military's use of drugs and helps the Department of Veterans Affairs procure drug contracts.

"Amid all of the media and public fascination with threats like Stuxnet and weighty terms such as 'cyberwar,' it's easy to overlook the more humdrum and persistent security threats, such as Web site vulnerabilities," Krebs wrote on his blog Friday. "But none of these distractions should excuse U.S. military leaders from making sure their Web sites aren't trivially hackable by script kiddies."

Robert McMillan covers computer security and general technology breaking news for The IDG News Service. Follow Robert on Twitter at @bobmcmillan. Robert's e-mail address is robert_mcmillan@idg.com